This invention concerns the stability of emulsions in general. As is well known in the art, emulsions may start to destabilise after a certain period of time. Emulsifiers when present may occur in either one or both phases. The separation process includes the steps of flocculation, coalescence (recombination of small droplets to larger droplets) and ultimately phase separation thereby forming a fully separated emulsion consisting of an upper oil layer and a lower aqueous layer. When the emulsion is a bitumen emulsion, this is different in that an aqueous top layer and a concentrated bitumen lower layer (often a sticky layer at the bottom which is very difficult to redisperse) are formed, because bitumen have a density at room temperature higher than the density of water.
The stabilisation of a two-phase emulsion involves decreasing the destabilisation rate which may be achieved by reducing the mobility of droplets dispersed in the continuous phase or liquid (i.e. by increasing the viscosity of the emulsion), by the insertion of an energy barrier between the droplets and the continuous phase or liquid, or both. Stabilisation is achieved by the addition of e.g. surfactants and polymers, also known as emulsifying agents.
Emulsions are employed in many industrial and food applications including cosmetic compositions, e.g. skin and hair preparations and make-up products, coatings and asphalt compositions. When used in asphalt compositions, these emulsions are usually composed of a bituminous binder and other components including an oil, an emulsifying agent and further additives such as a polymer as is well known in the art.
Emulsions of bituminous binders are frequently used in road construction and road repair. These emulsions are generally of the “oil-in-water” type and consist of a dispersion of an organic phase made up of small globules of the bituminous binder in a continuous aqueous phase, said aqueous phase containing an emulsifying system which promotes the dispersion of the small globules of the bituminous binder in the aqueous phase. The emulsifying system usually contains an emulsifying agent and optionally a pH regulating agent. The emulsifying agent may be anionic, cationic, non-ionic or amphotheric (or ampholytic). For example, U.S. Pat. No. 3,422,026, incorporated by reference herein, discloses besides emulsions comprising either anionic or cationic emulsifying agents, emulsions comprising amphotheric emulsifying agents. Making emulsions from a bituminous binder is a means to decrease the viscosity of the bituminous binder in operations wherein the bituminous binder is used and allows easy spraying. Emulsions of bituminous binders are fluids at ambient temperature and in the production of surface dressings a thickening agent is usually incorporated in the aqueous phase of the emulsion. The function of this thickening agent is to increase the viscosity of the emulsion to be spread on the support to be treated, so that the emulsion is kept in place on the support. Hence, before aggregate material or further asphalt layers are applied, a uniform layer of the emulsion on the support is guaranteed. Additionally, “cationic” emulsions are known in the art as having a pH of not more than 7 and contain cationic emulsifying agents, e.g. a fatty amine, whereas “anionic” emulsions are known in the art as having a pH of more than 7 and contain anionic emulsifying agents, e.g. a fatty acid metal salt.
Important properties of emulsions of bituminous binders are storage stability, processing properties, breaking properties and adhesive properties. Upon storage, emulsions tend to “break” or separate which is obviously undesired since they can then no longer be processed. However, common techniques for enhancing the storage stability of the emulsions often lead to poorer breaking properties, i.e. that breaking of the emulsion requires more time. It is well known in the art that when applied rapid and uniform breaking of emulsions of bituminous binders are advantageous for efficient workability, i.e. a short time to achieve breaking (full solidification) even under cold and humid weather conditions, which has the advantages that the treated road surface can be used shortly after a resurface of the road surface and that less damages occur during early use of the road surface.
Another problem in the art is that usually hard bituminous binders, in particular bituminous binders having a penetration according to ASTM D5-97 less than about 100 10−1 mm, require extensive stabilisation for storage, in particular for long-term storage. This extensive stabilisation also leads to poorer breaking properties.
U.S. Pat. No. 4,137,204, incorporated by reference herein, discloses asphalt emulsions containing polysaccharides, e.g. boiled corn starch, cellulose derivatives such as carboxymethylcellulose and hydroxyethyl cellulose, as thickening agents. An example of such a polysaccharide is Natrosol® 250 of Hercules.
U.S. Pat. No. 4,548,966, incorporated by reference herein, discloses an asphalt emulsion wherein a cross-linked starch is used as a thickener.
U.S. Pat. No. 4,879,326, incorporated by reference herein, discloses cationic emulsions that optionally comprise thickening agents selected from the group of water soluble natural gums and water soluble polyurethanes having a low molecular weight, i.e. below 20.000.
U.S. Pat. No. 5,246,986, incorporated by reference herein, discloses an emulsion of a bituminous binder wherein a thickening agent is employed that contains at least 40% by weight of scleroglucan, wherein it is preferred that the aqueous phase of the emulsion comprises 100 to 5000 ppm, preferably 200 to 2000 ppm of scleroglucan. Scleroglucan (CAS No. 39464-87-4) is known as a (1→3)-β-D-glucan having also (1→6)-β-D-linkages, wherein the polymer has glucopyranose side chains, and can be obtained from e.g. Sclerotinia sclerotiorum and Saccharomyces cerevisiae. The structural formula of scleroglucan is shown below for illustrative purposes:

Glucans are polymers of glucose and are commonly found in the cell walls of bacteria, fungi, yeast, and various plant species. A common glucan is a β-(1,3)-linked glucopyranose (commonly referred to as β-glucan). Other common examples include mixtures of β-(1,3)-linked glucopyranose with β-(1,4)-linked glucopyranose or β-(1,6)-linked glucopyranose.
Accordingly, there is a need in the art to provide emulsions in general and in particular emulsions of bituminous binders that have excellent storage stability and which break rapidly. There is also a need in the art to provide emulsions of bituminous binders which comprise hard bitumen and which still have excellent storage stability and which break rapidly upon application.
It is well documented that emulsion from harder grade bitumen can be applied as non-sticky tack or bond coats, i.e. the adhesive layer between two asphalt layers. The use of harder bitumen is causing less contamination of the environment as at ambient temperatures the broken bitumen emulsion will not stick to the tires of the asphalt trucks feeding the asphalt paving machine. Softer bitumen stick easily to truck tires at temperatures exceeding 30° C. and will subsequently cause black smears on the pavements surrounding the job. This causes a great nuisance especially when the asphalt trucks have to drive over coloured pavements, e.g. the popular red coloured bicycle lanes in the Netherlands (cf. for example US 2007105987, incorporated by reference).
In the southern part of Europe, 35-50 penetration grade bitumen is often used for non-sticky tack or bond coats. However, emulsions comprising such bitumen have to be handled with great care to avoid clogging and blocking of the nozzles of the tack coat spraying trucks. For example, it is regular practice that after a spraying job with non-sticky tack coat, the truck has to be discharged and sometimes even thoroughly cleaned to avoid clogging and sedimentation of the emulsion. It is obvious for experts in the field that harder grade bitumen will even cause more severe problems. Although 20-30 or even 10-20 bitumen are preferred during hot summers, the mediocre stability of these emulsions does not allow processing these materials in a practical and efficient manner.
As for example disclosed in U.S. Pat. No. 4,137,204, incorporated by reference, a bitumen emulsion can be stabilized with different polysaccharides as these materials act as thickeners. One of the important driving forces for sedimentation of bitumen emulsion is the density difference between the bitumen globules and the surrounding aqueous phase. Hence, the storage stability can be improved by increasing the viscosity of the aqueous phase which concomitantly increases the hydrodynamic frictional forces on the bitumen globules during sedimentation.
However, most of the commercially available cationic tack or bond coat emulsions have a pH close to 2. When stored at elevated temperatures, i.e. 50°-70° C., the molecular weight of the polysaccharides disclosed in U.S. Pat. No. 4,137,204 will drop due to acid catalyzed hydrolysis. A noticeable decrease in viscosity of polysaccharide-thickened bitumen emulsions is observed within a few days. Hence, it is favourable to use emulsion modifiers which are not or less sensitive towards acid catalyzed hydrolysis so that the emulsion demonstrates a constant quality for a prolonged period in time.
D. Bais et al., J. Colloid Int. Sci. 290, 546-556, 2005, discloses cosmetic 0/W emulsions comprising 0.2 to 1.2 wt. % scleroglucan.
S. C. Viñarta et al., Int. J. Biol. Macromol. 41, 314-323, 2007, discloses the use of gel matrices comprising 2 wt. % scleroglucan as drug delivery vehicles.
JP 2006-262862 discloses a cheese cake comprising a cheese head, a thickening stabilizer, an emulsion stabilizer and a gelling agent, wherein the emulsion stabilizer contains at least a polysaccharide. The polysaccharide is curdlan.
EP 619.079 discloses the use of curdlan as an emulsion stabilizer for enhancing dissolution of the outer coating of a feed additive composition. No amounts or ranges are mentioned.
EP 1.477.171 discloses the use of curdlan as emulsion stabilizer in a food additive. No amounts or ranges are mentioned.
U.S. Pat. No. 5,750,598 discloses that scleroglucan can be used as a viscosity-controlling additive in aqueous bitumen emulsions.
WO 2006/066643 discloses the use of choline esters in dermo-pharmaceutical and cosmetic products.